Heat radiation sensing device

ABSTRACT

A heat radiation sensing device is provided, which comprises two receiver surfaces which are exposed to the radiation, one of which comprises a high absorption ability with respect to the heat radiation by means of a black coloring, while the other has a low absorption ability by means of a covering which reflects the heat radiation. These two receiver surfaces consist of NTC resistor material and are combined to form a bridge circuit with two cermet resistors which are independent of temperature. The four resistors are applied to a ceramic substrate and are connected with conductor path which, in turn, end in the four required connections. The ceramic substrate is fixed in a frame which carries a covering which is pervious to heat radiation to a great degree and which, in turn, carries a layer having a window over one of the two NTC resistors the layer is made of a material which reflects the heat radiation to a great degree.

BACKGROUND OF THE INVENTION

The invention relates to a heat radiation sensing device. Such a sensingdevice has already been disclosed, for example, in "Sensor zum Messender Waermestrahlung an Arbeitsplaetzen," Technisches Messen, Ig. 51,1984, Heft 6, 8. 213 ff, in which two receiver surfaces consisting ofsheet copper are exposed to heat radiation, wherein each receiver sheetcomprises a temperature sensing device, which is glued to the rear side,so that the different temperatures, which occur due the fact that one ofthe receiver sheets is blackened and the other gold-plated, can bemeasured directly with this sensing device. The entirety is accommodatedin a housing consisting of brass. Because of the relatively complicatedconstruction, such a sensing device is not suitable for large-seriesproduction, which is the case, for example, in a sensing device which isto be used in a motor vehicle in connection with an air conditioningsystem.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an improved head radiationsensing device.

The heat radiation sensing device, according to the invention has theadvantage that it is simple to produce and, therefore, is also suitablefor large-series production, but is mechanically very stable. Moreover,it is small and light and can therefore be fixed at any requiredlocation, for example, by means of gluing. The arrangement provides asingle measuring signal which can be used in a simple manner, forexample, to control a shutter.

It is particularly advantageous that the covering, which is pervious toheat radiation, consist of a polyimide, e.g. a Kapton foil, which isprovided with a thin gold layer on one side by means of the applicationof a gold resinate and subsequent heat treatment at 300° to 350° C. Ifit is provided that the ceramic substrate on which the resistors arelocated is fixed in the frame in such a way that only the edge of thesubstrate is supported on a corresponding projection of the frame andthe remaining portion of the substrate is open, then a minimal effectiveheat capacity is achieved with good mechanical stability of thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the heat radiation sensing device and

FIG. 2 shows a section through the device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The heat radiation sensing device includes a frame 11 of duroplasticplastics material in which is located the ceramic substrate 5, whichcomprises two radiation-sensitive resistors 1 and 2, as well as tworesistors 3 and 4, which are not sensitive to temperature and areconnected with one another via conductor paths 6 in the form of a bridgecircuit. A portion of the ceramic substrate 5 projects from the frame 11and, together with the conductor path terminals 7, 8, 9 and 10, formsthe connection of the sensing device. Within the frame 11, the ceramicsubstrate, as shown in FIG. 2, is supported only by the edge 15 lying ona corresponding projection 16 of the frame 11 so that the major portionof the ceramic substrate 5 has no direct contact with the frame 11. Acovering 12, which is pervious, in its entirety, to heat radiation andcarries a layer 14 of noble metal on its rear side, is located on theframe 11 at a distance of approximately 1 mm from the ceramic substrate5, wherein this layer comprises a window 13 over the radiation-dependentresistor 1. By means of this, the resistor 1, which carries a blacklacquer layer, in addition, is exposed to the heat radiation, while thisis not true of the second radiation-dependent resistor 2 because of thereflecting noble metal layer 14. The covering 12 can be either formed ofa glass which is pervious to infrared radiation, e.g. Robax glass fromthe Schott company, or a polyimide foil, e.g. Kapton foil from theDupont company.

In order to produce the heat radiation sensing device the conductor pathpattern 6, with the connections 7, 8, 9 and 10, are first pressed on athin ceramic plate, preferably made of aluminum oxide. The NTC resistors1 and 2 are then pressed on, wherein a material is used, which is in theform of a paste and provides resistances which provide a rectangularresistance of 5 kΩ□ and a control constant B of 2200. The resistor pasteNTC 135 from the Heraeus company, for example, is suitable for thispurpose. Subsequently, the resistors 3 and 4, which are independent oftemperature, are applied in the same way, wherein a cermet material isused which provides a rectangular resistance of 10 kΩ□, the cermetmaterial with no. 1441 from the Dupont company. These resistor materialsare applied to the ceramic substrate with a thickness such that a layerthickness of 8 μm remains after burning in in air at 850° C. This bridgecircuit is now preferably adjusted to the cermet resistors 3 and 4 bymeans of a laser so that the bridge is currentless when a voltage isapplied to the connections 7 and 8. Subsequently, the ceramic substrate5 is inserted in the frame 11 and glued with the edges 15 on theprojections 16. Before applying the covering 12, the latter is coated onone side with a noble metal layer consisting, for example, of gold, inthat a layer of gold resinate is pressed on while leaving open a window13 which subsequently leaves a gold layer when burning in, which goldlayer adheres very favorably. When using glass, the burning intemperature is approximately 600° C.; if a Kapton foil is used, on whichthe gold layer, which is produced in this way, adheres in an excellentmanner, the gold resinate is burned in at 300° to 350° C. The covering12, with the gold layer 14, is then glued on to the frame 11 in such away that the window 13 is made to lie directly over the resistor 1,wherein this resistor 1 was covered with a black mat lacquer paint priorto the assembly. A bridge voltage of 12V, for example, is now applied tothe terminals 7 and 8, while an electric signal in the form of apotential can be taken off at the terminals 9 and 10 when there is heatradiation, since the resistor 1 changes as a function of the strength ofthe radiation to a greater degree than the resistor 2, which isprotected from the heat radiation by means of the reflecting layer 14.The bridge is accordingly adjusted, and the aforementioned outputsignal, which is a measurement of the incident radiation, occurs at theterminals 9 and 10. It has been shown that the output signal in mV ispractically a linear function of the radiation strength measured inW/m². This signal can now be used in a motor vehicle, for example, toactuate a shutter on the rear window when a determined radiationstrength is exceeded; naturally, such a heat radiation sensing devicecan also be incorporated in the control of an air conditioning system ofa motor vehicle.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofheat radiation sensing devices differing from the types described above.

While the invention has been illustrated and described as embodied in aheat radiation sensing device, it is not intended to be limited to thedetails shown, since various modifications and structural changes may bemade without parting in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A heat radiation sensing devicecomprising a ceramic substrate; two resistors formed by receiversurfaces positioned on said substrate and exposed to heat radiation, oneof the receiver surfaces (1) having a black coloring to provide thereona high absorption ability with respect to heat radiation, said tworeceiver surfaces (1) and (2) being made of NTC resistor material; twocermet resistors (3) and (4), which are non-responsive to temperatureand also positioned on said substrate, said two resistors forming withsaid cermet resistors on said substrate an electrical bridge circuit;conductor paths (6) provided on said substrate, said resistors (1) to(4) being connected with said conductor paths (6) a frame, said ceramicsubstrate (5) being fixed in said frame (11); and a covering (12) whichcovers said frame with said substrate therein and is pervious to heatradiation to a great degree and which carries a layer (14) on an innersurface thereof, which faces said substrate, said layer (14) being madeof a material which reflects heat radiation to a great degree and beingformed with a window which is positioned over said one of said receiversurfaces whereby another of said receiver surfaces is covered by saidlayer which reflects heat radiation.
 2. Heat radiation sensing deviceaccording to claim 1, wherein said resistors of NTC resistor materialhave a resistance of 0.5 to 500 kΩ□ at room temperature and a controlconstant B of approximately 2,200, while said cermet resistors (3, 4)comprise a resistance of 0.5 to 500 kΩ□.
 3. Heat radiation sensingdevice according to claim 1, wherein said covering (12) is made ofglass.
 4. Heat radiation sensing device according to claim 1, whereinsaid ceramic substrate (5) is fixed in said frame (11) in such a waythat only an edge (15) of said substrate (5) is supported on acorresponding projection (16) of said frame.
 5. Heat radiation sensingdevice according to claim 3, wherein said layer (14) is produced bymeans of pressing on said covering a layer of gold resinate andsubsequent burning in at predetermined termperatures.
 6. Heat radiationsensing device according to claim 5, said substrate being formed ofglass, said burning of said layer is performed at approximately 600° C.7. Heat radiation sensing device according to claim 5, said substratebeing formed of polymide, said burning of said layer being performed at300° to 350° C.
 8. Heat radiation sensing device according to claim 1,wherein said layer (14), which reflects the heat radiation, is made ofgold.
 9. Heat radiation sensing device according to claim 8, whereinsaid layer (14) is produced by means of pressing on said covering alayer of platinum resinate and subsequent burning in at predeterminedtemperatures.
 10. Heat radiation sensing device according to claim 1,wherein said covering (12) is made of polyimide.
 11. Heat radiationsensing device according to claim 1, wherein said layer (14) whichreflects the heat radiation is made of platinum.
 12. Heat radiationsensing device according to claim 1, wherein said ceramic substrate (5)and said covering (12) are assembled so that they have no directcontact.